1. Field of the Invention
This invention relates to turbines. More specifically, this invention relates to the engagement of blades onto discs or rotor discs of turbines.
2. Description of the Related Art
Steam turbines and rotors are constructed of discs or rotor discs that have a number of circumferentially disposed projecting steeples. During service, these steeples can be distressed in a number of ways. The steeples may incur mechanical damage from foreign objects. Also, the steeples are susceptible to stress corrosion cracking and pitting, corrosion, erosion corrosion, high cycle fatigue, and other factors. The environment in especially low pressure steam turbines, with all of its steam borne corroding components, promotes the corrosion of the steeples. These damage mechanisms evidence themselves by pitting and cracking the steeples and surrounding rim area, or substantial metal wastage thereof, and can lead to scrapping the entire rotor at great expense to the operator.
Now referring to Prior Art FIG. 1, the prior art discloses that the steeples on a disc 10 can be repaired by removing the distressed steeples and restoring the area with a solid weld metal buildup 12. The buildup 12 is then machined down to form a replacement steeple 14. A space 16 on disc 10 is where there was previously a distressed steeple that has been removed to prepare for another solid weld metal buildup.
The solid weld metal buildup method of steeple repair has prohibitive lead times and costs. A disc, particularly one used in a nuclear steam turbine which is more prone to stress corrosion cracking, may be as large as 100 inches in diameter. Repairing the steeples on an entire disc can take between 500 and 1000 hours. This time can be increased if weld defects are detected and corrected. Therefore, it is clear that a more economical method to repair the steeples is needed.